Copolymerization of vinyl compounds



Patented 17, 1946 COPOLYMERIZATION OF VINYL COMPOUNDS Edgar C. Brittonand Walter J.

land, Mich., assignors to Le Fevre, Mid- The Dow Chemical Company,Midland, Mich., a corporation of Michigan N Drawing. Application May 6,1944, Serial No. 534,530

14 Claims.

1 This invention concerns an improved method of preparing copolymers ofreadily polymerizable organic compounds each containing the radical:

Such polymerizable compounds are hereinafter referred to as vinyl andvinylidene compounds.

A copending application of J. W. Britton and R. C. Dosser, Serial No.351,222, filed August 3, 1940, discloses certain new and exceptionallyactive complex catalysts for the polymerization of vinyl and vinylidenecompounds and a method of polymerizing vinyl halides by means of suchcatalysts. The latter comprise as essential ingredients an acid, aperoxide, and a ferric salt of an inorganic acid.

However, in U. S. Patents 2,333,633 and 2,333,- 635 we have shown thatsuch complex catalyst, although effective in promoting thepolymerization of a. wide variety of vinyl and vinylidene compounds isunusually sensitive to the particular combinations of vinyl orvinylidene compounds and the reaction medium employed and that in orderto obtain most rapid polymerization when using the catalyst the kind ofreaction medium must be changed in going from the treatment of one vinylor vinylidene compound to the treatment of another. polymerization ofvinyl cyanide with such catalyst occurs far more rapidly when carriedout in the presence of aqueous methanol as a mutual solvent for thevinyl cyanide and catalyst than when attempted in an aqueous emulsion ofthe vinyl cyanide. In contrast, the polymerization of vinylidenechloride, i. e. asymmetric dich1oroethylene, with the catalysttakes-place more rapidly when carried out in an aqueous emulsion of thevinylidene chloride and catalyst than when carried out in an aqueousmethanol solution. Accordingly, in order to obtain best results whenpolymerizing individual vinyl or vinylidene compounds with thesecatalysts, a suitable medium must be selected.

We have found that such deliberate choice of a suitable reaction mediumis not required when employing the new complex catalysts to promote thecopolymerization of two or more vinyl and/or vinylidene compounds withone another. In fact, such catalytic copolymerization may frequently becarried out satisfactorily in the absence of solvents other than thepolymerizable compounds themselves. The explanation for this phenomenais not known with certainty, but apparently mixtures of two or morevinyl or vinylidene com- For instance, the 1 pounds are capable ofsimultaneously dissolving 0r absorbing all of the essential ingredientsof the complex catalyst, e. g. to form a. true, or a colloidal, solutionof the catalyst ingredients. Most individual vinyl or vinylidenecompounds do not possess this property except in the presence of amutual solvent for the polymerizable compound and the catalyst.

The presence of a liquid medium is usually advantageous even whencopolymerizing two or more vinyl or vinylidene compounds with thecomplex catalyst, but the selection of a suitable medium is lessdifficult when carrying out such copolymerization than when polymerizinga single vinyl or vinylidene compound with the catalyst.

We have further found that when the copolymerization of different vinyland/or vinylidene compounds is carried out using a complex catalystcomprising an acid, a peroxygen compound and a ferric salt of aninorganic acid to promote the reaction, the molecular ratio between thedifferent polymerizable compounds making up the copolymer productcorresponds more closely to the ratio in which said compounds wereemployed as reactants than when the copolymerization is carried outunder otherwise similar conditions, except that the ferric salt(employed as a catalyst ingredient) is omitted.

As hereinbefcre indicated, the complex catalysts employed in the presentprocess consist essentially of an acid, a peroxygen compound capable ofsupplying nascent oxygen to the polymerization mixture, and a ferricsalt of an inorganic acid. The kinds and relative proportions of acid,peroxygen compound, and ferric salt may be varied quite wide1y.-However, there are definite limits as to the proportions of acid orferric salt which should be employed in order to obtain a strongcatalytic effect.

Any acid capable of rendering the reaction mixture sufliciently acidic,e. g. a mineral acid such as nitric acid, hydrochloric acid, sulphuricacid, etc., may be employed as the acid ingredient of the catalyst. Inmost instances nitric acid is preferred, since it appears to be somewhatmore effective than the other acids. It is important that the acid bepresent in amount suflicient to give the polymerization mixture a pHvalue of less than 3, since the activity of the complex catalystdecreases sharply with increase of the pH value above 3. The acid ispreferably used in amount suflicient to give the reaction mixture a pHvalue between 1.5 and 3.

As the peroxygen ingredient of the catalyst,

hydrogen peroxide is preferred. However, other peroxygen compounds suchas benzoyl peroxide, sodium perborate, peracetic acid, or metalperoxides such as barium, or sodium peroxide which will react with theacid to form hydrogen peroxide in situ may be used. Between 0.002 and0.2 mole of peroxide is usually employed per mole of the polymerizablecompounds, but the peroxide may be used in smaller or considerablylarger proportions if desired The presence of a large excess of aperoxygen compound over the amount necessary to obtain the catalyticeffect is not detrimental.

Any ionizable iron salt of an inorganic acid may be used as aningredient of the complex catalyst. The iron salt may be added as suchor be formed in situ within the polymerization mixture, e. g. by addingthe iron as ferric oxide and reacting the latter with a portion of theacid added as a catalyst ingredient. Examples of suitable ferric saltsare ferric nitrate, ferric chloride, ferric sulphate, ferric bromide,etc. The ferric salt is usually employed in amount such that its ironcontent corresponds to between 0.0001 and 0.05 per cent of the combinedweight of the vinyl and/or vinylidene compounds. .However, it may beused in smaller or in somewhat larger proportions if desired.

From the foregoing it will be seen that the relative proportions of theessential catalyst ingredients may be varied over wide ranges. However,in most instances we prefer to employ the ferric salt and the peroxidein proportions corresponding to between 0.000001 and 0.0004 gram atom ofiron (in the ferric salt) .per mole of the peroxide.

As hereinbefore stated, the copolymerization of two or more vinyl and/orvinylidene compounds with the above-described complex catalyst may becarried out in the absence of any medium other than the polymerizablecompounds themselves, but is advantageously carried out either in thepresence of a solvent for the polymerizable compounds and the catalystor in aqueous emulsion. In any instance it is preferably, though notnecessarily, carried out in a closed reactor or in contact with an inertatmosphere, e. g. nitrogen or carbon dioxide, so as to avoid possiblediscoloration of the product by air. When operating without an addedreaction mediumjthe several catalyst ingredients and the polymerizablecompounds in the proportions hereinbefore stated are mixed and themixture is brought to and maintained at a polymerizing temperature untilthe reaction is substantially complete. The temperature required forrapid polymerization varies somewhat depending upon the particularpolymerizable compounds used, but in most instances the catalyticcopolymerization occurs rapidly at temperatures between 20 and 100 C.and in some instances it may be carried out at temperatures as low as C.It may, of course, be carried out at temperatures up to thedecomposition point of the product, e. g. at 150 C. or higher.

When carrying the copolymerization out in solution, the vinyl and/orvinylidene compounds and the essential catalyst ingredients in theproportions hereinbefore stated are dissolved in a solvent. and thesolution is brought to a polymerizing temperature, e. g. usually to atemperature between and 100 C. As the solvent, aqueous methanol ofbetween 60 and 90 per cent by weight concentration is usually employed,but other solvents for the polymerizable compounds and the catalyst,such as dioxane, acetone, aqueous ethanol, etc., may be used. Aftercompleting the polymerization, the copolymer is separated in any of theusual ways, e. g. by adding water to precipitate the product when awater-soluble solvent has been used as the reaction medium, or bydistilling the solvent from the product, preferably under vacuum. Inmany instances, the co- A polymer products solidify as they are formedand may be separated mechanically, e. g. by decantation or filtration.

When conducting the catalytic copolymerization in aqueous emulsion, thepolymerizablecompounds and catalyst ingredients are employed in therespective proportions hereinbefore stated and the polymerization ispreferably carried out at temperatures within the ranges hereinbeforegiven. The emulsion is prepared by mixing the polymerizable compoundsand the catalyst ingredients with an aqueous solution of an emulsifyingagent and agitating the mixture until it is emulsified. The identity ofthe emulsifying agent is of little importance, but it must, of course,be one capable of forming stable emulsions with the acidic mixturesemployed. A variety of emulsifying agents having the property of formingstable emulsions of organic compounds with dilute aqueous acids are wellknown. Among the various emulsifying agents which may be used are eggalbumen and alkali metal sulphonates of aliphatic and alkyl-aromatichydrocarbons of high moleculr weight. Nopco (a sodium salt ofsulphonated sperm oil) is particularly well adapted to use as theemulsifying agent.

After completing the copolymerization in emulsion, the emulsion isbroken in any of the usual ways, e. g. by heating the same, or by addingmethanol, ethanol, propanol, acetone, ammonia, or water-soluble saltssuch as sodium chloride, whereby the copolymer isprecipitated, usuallyas a powder. The precipitate is separated from the liquor, washed freeof adhering mother liquor and dried.

The following table describes the operating conditions employed and theresults obtained in a number of tests .on the copolymerization of vinyland/or vinylidene compounds with one another in the presence of thecomplex catalysts. Certain of the tests were carried out in the absenceof any medium other than the polymerizablecompounds themselves; otherswere carried out in aqueous methanol solutions; and still others werecarried out in aqueous emulsion using Nopco (the sodium salt ofsulphonated sperm oil) in amount corresponding to 10 per cent of thetotal weight of the polymerizable compounds as the emulsifying agent.For purpose of comparison, the table includes not only the experimentswherein the copolymerization was carried out in the presence of thecomplex catalyst, comprising an acid, a peroxide, and a ferric compound.which is required by the invention, but also other experiments whereinthe acid and peroxide were used, but the ferric compound was omitted. Inall of the experiments, regardless of how they were carried out,hydrogen peroxide in amount corresponding to 2 per cent of the totalweight of the polymerizable compounds and nitric acid in amountsufficient to reduce the pH value of the mixture to approximately 2,were present.

In those experiments wherein a ferric compound also was present, ferricchloride was used in amount corresponding to 0.004 per cent of theweight of the entire mixture. Each copolymerization was carried out byheating the reaction mixture in a closed container under thepolymerizing conditions stated. The table names and gives theproportions, inparts by weight, of the vinyl or vinylidene compounds andthe liquid medium employed, indicates whether or not a ferric compound,i. e. ferric chloride, was present in the mixture, gives the conditionsof time and temperature employed in eifecting each polymerization andgives the p r cent yield of polyamount sufilcient to give thepolymerization mixture a pH value between about 1.5 and about 3, theperoxygen compound, ferric salt and acid each being dispersed within thepolymerization mixture.

2. In a method wherein different polymerizable organic compounds, eachcontaining the radical:

merized product, based on the vinyl and vinnlo=o ylidene compoundsemployed. l0

Table Medium Polymcrizable compounds g d R N Nature of F8013 un runpresent De Tem Time cent Kind Parts Kind Parts Kind Parts 0 1 No mediumNone vinylidene chloride. 50 Vinyl cyanide 50 No 40 7 2 do -do -do 50 d050 Yes 40 7 27. 5 3 In solutionv sfgficonc 50 Vinyl chloride 25 No 40 llTrace 4 d 25 Yes 40 11 80. 5 5 42. 5 Yes 40 ll 71. 0 6 3. 75 No 40 17 1675 do 3. 75 Yes 40 17 92 75 .do 12. 5 Yes 40 17 95 75 Vinylidenechloride 3. 75 No 40 17 57 75 do 1. 3. 75 Yes 40 17 100 75 do l2. 5 Yes40 17 100 In the foregoing table, runs Nos. 2, 4, 5, 7, 8, 10, and 11show that the complex catalyst comprising an acid, a peroxide, and aferric compound is effective in promoting the copolymerization of vinyland or vinylidene compounds with one another even though the kinds ofpolymerizable compounds employed and the other polymerizing conditionsbe varied widely. Comparisons of run 1 with 2, of run 3 with run 4, ofrun 6 with run '7, and of run 9 with run 10 demonstrate that saidcomplex catalyst (which comprises a ferric compound) is far moreeffective than is a mixture of only the acid and peroxide in promotingthe copolymerization. Other vinyl and vinylidene compounds which mayadvantageously be copolymerized with one another in the presence of thecomplex catalyst are methyl methacrylate and vinyl cyanide; vinylchloride and vinyl acetate; vinylidene chloride and methylalpha-methyl-vinyl ketone, etc. The complex catalyst is apparentlyeffective in promoting the copolymerization regardless of the identityof the vinyl or vinylidene compounds used in the reaction.

This application is a continuation-in-part of our copending applicationSerial No. 351,222, filed August 3, 1940.

Other modes of applying the principle of our invention may be employedinstead of those explained, change being made as regards the materialsemployed, provided the ingredients stated by any of the following claimsor the equivalent of such stated ingredients be employed.

We therefore particularly point out and distinctly claim as ourinvention:

1. In a method wherein difierent polymerizable organic compounds, eachcontaining the radical:

are copolymerized, the step of catalyzing the polymerization reaction bycarrying it out in the presence of a minor amount of a dispersed complexcatalyst consisting essentially of a peroxide, a ferric salt of aninorganic acid in amount having an iron content corresponding to betweenabout 0.0001 and about 0.05 per cent of the com- -'bined weight of thepolymerizable organic compounds and an acid in amount sufficient to givethe polymerization mixture a. pH value between 1.5 and 3.

3. The method as described in claim 2, wherein the peroxide is hydrogenperoxide.

4. The method as described in claim 2, wherein the peroxide is hydrogenperoxide and the acid is nitric acid.

5. In a. method wherein different polymerizable organic compounds, eachcontaining the radical:

are copolymerized, the step of carrying the polymerization out .in thepresence of a dispersed complex catalyst consisting essentially of anacid in amount sufficient to give the polymerization mixture a pH valuebetween 1.5 and 3, between 0.002 and 0.2 mole of a peroxide per mole ofthe polymerizable compounds, and a ferric salt of an inorganic acid inamount such that its iron content corresponds to between 0.0001 and 0.05per cent of the combined weight of the polymerizable compounds.

6. In a method wherein difierent polymerizable organic compounds, eachcontaining the radical:

are copolymerized while dissolved in a solvent, the step of catalyzingthe polymerization by carrying it out in the presence of a dispersedcomplex catalyst consisting essentially of a peroxide, a ferric salt ofan inorganic acid in amount having an iron content corresponding tobetween about 0.0001 and about 0.05 per cent of the combined weight ofthe polymerizable organic compounds, and an acid in amount sufiicient togive the polymerization mixture a pH value between about 1.5 and about3.

7. The method which comprises dissolving in an inert solvent differentpolymerizable organic compounds, each containing the radical:

and a minor amount of a complex catalyst consisting essentially ofhydrogen peroxide, a ferric salt of an inorganic acid in amount havingan iron content corresponding to between about 0.0001 and about 0.05 percent of the combined weight of the polymerizable organic compounds, andan acid in amount sufiicient to give the polymerization mixture a pHvalue between about 1.5 and about 3, and copolymerizing thepolymerizable com ounds while in said solution.

8. The method which comprises dissolving in aqueous methanol differentpolymerizable organic compounds, each of which contains the radical:

and a minor amount of a complex catalyst consisting essentially ofhydrogen peroxide, a ferric salt of an inorganic acid in amount havingan iron content corresponding to between 0.0001 and 0.05 per cent of thecombined weight of the polymerizable organic compounds, and nitric acidin amount suflicient to give the polymerization mixture a pH valuebetween 1.5 and 3, copolymerizing the polymerizable compounds while insaid solution and separating the polymerized product.

9. The method which comprises forming an aqueous emulsion containing indispersed form different polymerizable organic compounds, each of whichcontains the radical:

a minor amount of peroxide, a ferric salt of an inorganic acid in amounthaving an iron content corresponding to between 0.0001 and about 0.05per cent of the combined weight of the polymerizable organic compounds,and an acid in amount suificient to give the emulsion a pH value betweenabout 1.5 and about 3, and copolymerizing the polymerizable compoundswhile in the emulsion.

10. The method which comprises forming an aqueous emulsion containing indispersed form difi'erent polymerizable organic compounds, each of whichcontains the radical:

between 0.002 and 0.2 molecular equivalent of hydrogen peroxide per moleof the polymerizable compounds, a ferric salt of an inorganic acid inamount having an iron content corresponding to between 0.0001 and 0.05per cent of the combined weight of the polymerizable compounds and anacid in amount sufficient to give the emulsion a pH value between 1.5and 3 and copolymerizing the poylmerizable compounds while in theemulsion.

11. The method which comprises polymerizing a mixture of methylmethacrylate and vinylidene chloride in the presence of a minor amountof a dispersed complex catalyst consisting essentially of a peroxide, aferric salt of an inor ani acid in amount having an iron contentcorresponding to between 0.0001 and 0.05 per cent of the combined weightof the methyl methacrylate and vinylidene chloride, and an acid inamount sufficient to give the mixture a pH value between 1.5 and 3.

12. The method which comprises forming an aqueous emulsion whichcontainsin dispersed form methyl methacrylate, vinylidene chloride, aminor amount of a peroxide, a ferric salt of an inorganic acid in amounthaving an iron content corresponding to between 0.0001 and 0.05 per centof the combined weight of the methyl methacrylate and vinylidenechloride, and an acid in amount sufficient to give the emulsion a pHvalue between 1.5 and 3, copolymerizing the methyl methacrylate andvinylidene chloride while in the emulsion, and separating thepolymerized prodnot.

13. The method which comprises copolymerizing vinylidene chloride andvinyl cyanide in the presence of a minor amount of a peroxide, a ferricsalt of an inorganic acid in an amount such that its iron contentcorresponds to between 0.0001 and 0.05 per cent of the combined weightof the vinylidene chloride and vinyl cyanide, and an acid in amountsufficient to give the mixture a pH value between 1.5 and 3, theperoxide, ferric salt and acid being dispersed together with thecompounds being polymerized.

14. The method which comprises forming an aqueous emulsion whichcontains vinylidene chloride and vinyl cyanide, a minor amount of aperoxide, a, ferric salt of an inorganic acid in amount such that itsiron content corresponds to between 0.0001 and 0.05 per cent of thecombined weight of the vinylidene chloride and vinyl cyanide, and anacid in amount sufiicient to give the emulsion a pH value between 1.5and 3, and copolymerizing the vinylidene chloride and vinyl cyanidewhile in said emulsion.

EDGAR C. BRI'ITON. WALTER J. LE FEVRE.

